1. Field of the Invention
The present invention relates to an automatically shiftable countershaft transmission for motor vehicles. More specifically, the invention relates to varying the shift force as a function of the gear step and the dynamic load (Ldyn) over the engagement travel (WE) in such a way that, depending on the functional phase, a lower force is provided during the synchronization phase, a higher force is provided during the shift-through phase, and a lower force is provided during the dog-in phase.
2. Description of the Related Art
British patent specification 1 281 106 discloses an automatically shiftable countershaft transmission, particularly for motor vehicles. The transmission casing houses a plurality of gearwheel pairs which are constantly in mesh with one another and can be selectively connected to their respective shafts by means of dog clutches. The dog clutches are actuated by means of electronically controlled hydraulic servo devices in order to effect automatic gear shifts as a function of the operating parameters of the driving engine and of the motor vehicle. All necessary components such as hydraulic pumps, actuating cylinders and the like are included in a constructional unit which can be attached to the transmission casing.
This transmission has the inherent disadvantage of only using dog clutches to shift into the individual gear steps. An accelerating and retarding unit must be provided on the countershaft and must be further controlled in dependence on speed sensors. The dog clutch elements which are to be brought into engagement with one another must therefor be synchronized before the engagement of the gear steps can take place.
In the periodical "Automobil-Revue" No. 16 of Apr. 15, 1993, "Auf den Spuren von Senna, Prost & Co. (In the footsteps of Senna, Prost & Co.)" there is a report of an automatically shiftable countershaft transmission, particularly for motor vehicles. A plurality of gearwheel pairs which are constantly in mesh with one another are disposed in a transmission casing and can be brought into engagement with one another through synchronizing devices. The actuation of these synchronizing devices takes place through an electronic control module by means of a cam control unit. No detail is provided as to the arrangement of the servo device.
In the periodical "Automobil-Revue" No. 12 of 17.03.1994 "Schalten wie in Formel 1 (Change gear as it's done in Formula 1)" there is a report about automatically shiftable countershaft transmissions in which it is stated in general terms that an electronic control module actuates the pneumatic servo device so that gear shifting is undertaken with deliberate care for the synchronizing devices. No detail is provided as to the manner in which this sensitive actuation is effected.
It is desirable to provide an automatically shiftable countershaft transmission, particularly for motor vehicles, which is based on a mass production manual transmission which can be converted to an automatically shiftable countershaft transmission which does not place undue demand on the synchronizing devices within the transmission.